1. Field of the Invention
The present invention relates to the hydroxylation of phenols and phenol ethers, and, more especially, to the hydroxylation of phenols and phenol ethers by reaction with hydrogen peroxide.
2. Description of the Prior Art
French Patent No. 69/45,467, published under U.S. Pat. No. 2,071,464, describes a process for the hydroxylation of phenols and phenol ethers using hydrogen peroxide, in the presence of a strong acid catalyst. Exemplary of such strong acids are sulfuric acid, paratoluenesulfonic acid and perchloric acid.
The process of this '467 patent is very significant commercially. Nonetheless, this art has long sought an alternative catalytic process wherein the catalyst would be less corrosive for the apparatus employed.
Thus, published French Patent Application FR-2,489,816 specifies the use of silicalites of various metals for such purpose.
And published European Patent Application EP-A-0,299,893 describes the use of bridged clays.
Although these processes which employ heterogeneous catalysis would appear to be desirable alternatives, it has transpired that, on the one hand, industrial-scale problems such as the recycling of the catalyst still exist and that, on the other, the efficacy thereof is not fully on the level of the process employing a strong acid catalyst.